The goal of this research is to understand the processes that induce, regulate and pattern development and morphogenesis of the Drosophila dorsal air sacs (DAS). Our work has shown that Bnl-FGF induces this large, complex and multi-lobed tracheal organ which functions in ways that are analogous to the vertebrate lung. This organ ventilates the adult fly and supplies oxygen to its flight muscles. Its development offers a powerful system to study the pathways that lead to organ induction, growth and patterning. Specific aims are proposed to: (1) gain a detailed description of the development and morphology of the DAS;(2) identify and analyze genes expressed at various stages and at different locations in the DAS;and (3) identify and characterize mutants defective in DAS development.